The city, which is in the center of the state's tech hub, is conducting experiments to see if it can cut energy consumption and maintenance costs by replacing conventional public light fixtures with ones based around light-emitting diodes.

In December, Raleigh--in conjunction with LED manufacturer Cree--replaced high-pressure sodium lights in a downtown parking garage with LED lights. Although the LED lamps cost substantially more than regular sodium lamps, they require less electricity and need to be replaced far less often.

Early projections indicate that the expense of retrofitting the garage's lighting system will get recovered in cost savings in two to three years, said Mayor Charles Meeker.

"We are saving over 40 percent of the energy we would otherwise use," said Meeker, who's currently on his third two-year term. "And the quality is better. With sodium lights, you get bugs in the cover, and the light is kind of yellowish."

Next, Raleigh will kick off a pilot program with LED streetlights and will also seek funds to convert the city's other parking garages. If all seven municipal parking lots in the city were retrofitted, it could save the city $100,000 a year in energy consumption and decreased maintenance, he said. The lights in stadiums, gyms, schools, parks and other public venues could be next.

If successful, the experiment could ultimately serve as a showcase for something several LED manufacturers are angling to accomplish: maneuvering LEDs into the commercial and residential lighting market. LEDs are used in flashlights and car headlights and taillights, but commercial and residential lighting represents a much larger opportunity. Approximately 22 percent of the electricity consumed in the United States goes toward lighting, according to the U.S. Department of Energy.

LEDs can last 75,000 hours or longer and consume far less power than standard incandescent bulbs. Only about 5 percent of the energy that goes into conventional bulbs actually turns into light; the rest gets dissipated as heat. If 25 percent of the lightbulbs in the United States were converted to LEDs putting out 150 lumens (a measure of light output) per watt--higher than the most current models--the country as a whole could save $115 billion in utility costs cumulatively by 2025, according to University of California Santa Barbara professor Stephen DenBaars.

LEDs also have begun to outperform fluorescent bulbs in energy efficiency, said Cree CEO Chuck Swoboda. The company last year unveiled an LED that can put out about 70 lumens per watt. That's a bit better than many compact fluorescent bulbs--those cone-shaped things that fit into regular light fixtures--on the market, which often get 60 lumens per watt.

The problem up until now has been cost. Consumers and businesses can buy lighting fixtures based around LEDs now, but the price is high compared with other types of lights. While fluorescent manufacturers dispute many of the energy efficiency claims by the LED industry, they also note that their products cost far less.

The rising cost of electricity, combined with the declining prices of LEDs, however, is making diodes more attractive to manufacturers of lighting fixtures, Swoboda said. Over the next year, LED-based light fixtures for commercial buildings and signs will begin to increase in number, he said. The commercial market in many ways is inherently more attractive because they don't need to be replaced as often, which cuts down the number of times the maintenance crew has to put up a ladder.

"When you get into lights that are on 24-7, the maintenance costs certainly go up. LEDs are going to find their ways quicker there than other markets," Swoboda said. "The home is not typically mission critical."

Nonetheless, he added that LED lights would likely begin to appear in new homes in six months to a year. Contractors can absorb the cost in the overall price of the home.

Making an LED light fixture stronger or less bright is largely a matter of how the fixture is designed and the number of LEDs inside. A lawn light based around LEDs might have two of the diodes inside, said Swoboda; a light for a garage might have 84.

LEDs emit red, blue or green light on their own. To make white light, the light from blue LEDs passes through a yellowish phosphor.